1. Field of the Invention
The present invention is generally directed toward endoscopes and, more particularly, toward image transmission devices used in endoscope optics.
2. Description of Related Art
Endoscope optics conventionally include a proximal image viewing system, for instance an ocular or a camera, and a tubular stem with an objective fitted into its distal end. The endoscope also includes an image transmission device that is disposed between the objective and the image viewing system. The image transmission device consists of several optical lenses. These optical lenses are almost always thick rod-shaped lenses that are spaced apart from one another inside the stem.
Many applications require endoscope optics of minimal stem diameters. In particular as regards such narrow optics, but also in general endoscope optics, a problem arises in that the lens elements used for image transmission are easily damaged because of their particular geometries. Minor shocks or bending stresses applied to the stem may break or chip the lens elements. Repairs are very costly and in most cases the entire stem must be replaced.
Accordingly, there exists a need in the art for an endoscope optics system that is substantially more resistant to shocks and bending stresses, and that will therefore be more durable.
The present invention is directed toward an endoscope optics having image transmission devices that are substantially more resistant to damage from shocks and bending stresses.
In accordance with one aspect of the invention, the optical elements of the image transmission device are made in part or in whole of sapphire.
Compared with conventional optical glass, sapphire offers a number of advantages. One essential advantage is its mechanical strength which, compared to conventional optical glasses, offers a substantially higher resistance against breakage or chipping.
Moreover, sapphire exhibits a relatively high index of refraction. Lens elements offering good imaging properties may be made at comparatively low cost from sapphire. Also, lens elements with spectral transmission properties may be made within a wide range of wavelengths by resort to simple anti-reflection coatings.
Endoscope optics are known from WO 99/19752 of which the distal objective lenses are made of sapphire. Sapphire was used to improve the optical properties of the objective lens. On the other hand, conventional optical glass incurring the above-cited drawbacks was used for the image transmission devices described in WO 99/19752.
As a rule, several rod-shaped thick lenses are used in conventional image transmission devices and also in the image transmission devices of the present invention. The rod-shaped thick lenses implement the image transmission through the stem over a large portion of the optical path. The thickness of the rod-shaped lens elements is a multiple of its diameter and explains their special susceptibility to mechanical stresses.
Besides the aforementioned rod elements, one or more optical correcting lens elements may additionally be used in the transmission path in order to compensate for any chromatic aberration or the like. These corrective elements are made of a glass other than that used for the rod lenses and their thickness is substantially less.
Accordingly, a preferred embodiment of the invention provides that the image transmission devices of endoscope optics comprise several different kinds of lenses of which only those that are especially susceptible to breaking or chipping on account of their geometries shall be made of sapphire, whereas the corrective lenses used to compensate any optic defects in the transmission path and which are less susceptible being made of another optic glass.
Conceivably again, compound lens elements such as a plano-convex thick lens made of sapphire and a further and thinner plano-convex lens made of another glass might be used in the image transmission device, both lens elements abutting each other by their plane surfaces and for instance being bonded together.
These and further features of the invention will be apparent with reference to the following description and drawing wherein an illustrative embodiment of a distal end an endoscope according to the present invention is shown.